Method of producing tear resisting rubber sheeting



June 3, 1941, A. N. IKNAYAN METHOD OF PRODUCING TEAR RESISTING RUBBER SHEETING Original Filed Oct. 8, 1937 INVENTOR. AZf/fffl A4 /f/V4/4/V BY 5 Z [3 4 g 7 L ATTORNEYS Patented June 3, 1941 I METHOE) F PRODUG'IN G TEAR, RESISTING RUBBER SHEETYING Alfred N. Iknayan, Indianapolis, Ind., assignor, by mesne assignments, to United States Rubber Company, New York, N. Y., a corporation of New Jersey Original application October 8, 11937, Serial No.

i167,938. Divided and this application September 24, 1938, Serial No. 231,528

(Cl. Iii-59) 3 Claims.

This invention, a divisional application of application Serial No. 167,938, filed October 8, 1937, relates to methods of producing tear resisting rubber articles, and in particular it relates to appear more fully in the following detailed description of a preferred embodiment of the invention and with reference to the drawing in which:

inner tubes having walls of rubber characterized Fig. 1 is a perspective view of a sheet of rubber by the feature of limiting the length of tears embodying the features of the invention; that might occur in the inner tube wall. Fig. 2 is a perspective view, partly broken away,

In general, the invention provides an arrangeof the sheet in the process of manufacture; ment of separations extending partly through the Fig. 3 is a perspective view, in section, of an wall of a rubber article, whereby tears which in inner tube showing features of the invention emreach the separations are hindered from proceedbodied therein; and ing further in view of the difficulty of originat- Fig. 4 is a perspective view, in section, of an ing tears at the marginal wall of the separation. inner tube, illustrating a modification of the When a tear or cut is initiated in a sheet of inner tube shown in Fig. 3. vulcanized rubber there is a tendency for the Referring to the drawing, and in particular to tear to increase rapidly with but very little strain Fig. 1, I show an embodiment of the invention in in the rubber. It is considerably more difficult the form of a sheet of rubber I having a plurality to start a tear at the edge of a sheet of vulof separations 2 in the form of circular paths, the canized rubber than it is to increase the length of axes of which extend substantially in a transthe tear after it is started. By utilizing this verse manner relative to the plane of the sheet characteristic, I break up the continuity of the of rubber I. The separations 2 forming the cirsheet of rubber through the incorporation therein cular paths extend in depth to about one-half of separations which, in effect, function as marof the thickness of the sheet of rubber l. Effecginal edges and as such resist continuation of a tive results may be obtained by having the sepatear. rations extend to a depth of at least one-fourth In mounting inner tubes and tire casings in of the thickness of the sheet, and not in excess assembly with a tire rim, particularly a rim of of three-fourths of the sheet thickness. The the drop center type, it frequently occurs that number and arrangement of the circular paths the inner tube is partially inflated before the tire are such that a tear originating in any part of is in full engagement with the bead seats of the the strip and running in substantially a straight rim. As a result of this condition, the tube beline should enga e W O e O the Sepa at ons, comes stretched excessively at localized portions, resulting in greater resistance of the sheet of which stretched condition is not entirely rerubber against continuation of the tear. Ihave lieved upon completion of the mounting of the found that, by staggering the various rows of assembly. Thereafter, when the tube is in opercircular paths, a tear when initiated will comation failure is likely to occur in such excessively municate with one of the separations before the stretched zones. Complete failure of the tube tear becomes comparatively long. may be originated by the pinching between the In order that the fabrication, construction and tire bead and the rim, by blow-outs, or by function of the tear resisting material may be chafing conditions resulting from irregularities understood, reference may be made to Fig. 2 in the tire fabric. which illustrates a strip of the material in process In such inner tube failures a small tear or of manufacture. puncture occurs in the wall of the tube, and due The strip I comprises a base layer 3 and a to the force of the compressed air passing out of p rf l ye Both layers are of unvulthe tube and the tendency of the tube to tear canized rubber, and may be of the same material easily after the tear originates, the resultant concomposition, although effective results may be dition of the tube, is such that. the tear is too obtained by forming the perforated layer 4 of long to permit of satisfactory repair. a rubber stock having tougher characteristics. It is, therefore, among the objects of the in- This will increase the tear resisting quality of vention to produce and provide a sheet of rubber the sheet. having characteristics which will function to The perforated layer 4 is provided with a pluminimize the tearing of the sheet, and to provide rality of holes or perforations 5 extending an inner tube capable of being satisfactorily rethrough the layer of rubber. These perforations paired in the usual manner after failure. 5 are formed in the layer 4 prior to the applica- These and other objects and advantages will tion of the layer 4 to the base layer 3. Any suitforatlons 5.

able means, such as a punching operation, may be employed to make the perforations in the layer 4. The perforated layer 4 is placed in laminated relation with the base layer 3 while the layers are in their unvuloanized state. Under this condition, the layer 4 will adhere readily to the layer 3. If desired, the layers may be rolled together to insure proper adhesion.

After the layers 3 and 4 .are properly adhered together, the laminated sheet thus formed is subjected to lubrication, i. e., the adhesive characteristic of its exposed surfaces is reduced. A practical means of accomplishing this result is to subject the laminated sheet to a dusting operation with a medium such as powdered soapstone or mica. In the dusting operation the walls of the perforations 5 are well coated with the dusting medium, so that during subsequent operations" they will not substantially adhere to rubber flowing from the base layer 3.

In the next operation the strip l formed of the laminated layers 3 and t is vulcanized'under heat and pressure. Preferably, the perforated layer 4 is placed adjacent the mold surface and pressure exerted against the exposed surface of the base layer 3. While this is the preferred method of placing the strip in the vulcanizing mold, it is obvious that various combinations of directing pressure and positioning the strip within the mold will operate to accomplish results which are substantially satisfactory.

Due to the application of the lubricating material, such as soapstone, the rubber of the base layer 3 will not merge with the walls of the pervulcanization between the different rubber layers may take place at the walls of the perforations. Upon vulcanization, the principal adjoining surfacesof the layers 3 and 4 merge together to form a unitary sheet of rubber. As shown in Fig. 1, a sheet of rubber is formed having a plurality of circular paths defining lines of demarcation between the different layers of rubber composition. When the rubber sheet is under extension any union between the rubber compositions at the walls of the perforations becomes broken, with the result that the circular paths define separations. 'Any union that may exist between the rubber compositions at the circular paths is broken with much less strain in the rubber than that required to produce a tear in rubber.

When the under side or exposed surface of the base layer 3 is subjected to fluid pressure, as distinguished from confinement in a mold, a plurality of indentations 6 are formed in complementary relation with the perforations. This is due to the flowing of rubber stock from the tending over one-half of the tube when measured :1

transversely.

The tear resisting layers may be applied to the tread side only of the inner tube or it may be applied to the entire surface of the inner tube, such as shown by the inner tube 8 in Fig. 4.

In manufacturing inner tubes having a tear resisting layer of rubber, the embodiment may be manufactured by extruding the inner tube in the usual manner and thereafter applying a perforated layer to the outer surface of the tube.

However, an adherence or slight After this operation, the conventional practice of manufacturing inner tubes may be followed; that is, the tubes are spliced, dusted with soapstone, and vulcanized in conventional inner tube molds.

The laminated layers 3 and 4 as shown in Fig. 2 are representative of the tear resisting formation of the inner tubes. As thus applicable to finished inner tubes, I find the preferred thickness of the base layer 3 to be in the order of .055 inch, and the preferred thickness of the perforated layer 4 to be .040 inch. After vulcanization, and due to the flow of rubber from the base layer 3 into the perforations, the approximate thickness of the laminated sheet is in the order of .075 inch.

Good results in restricting the tearing of inner tubes may be obtained by providing at least eight perforations per square inch. however, to increase the number of perforations to about eighteen perforations per square inch. This may be accomplished by providing holes of a diameter of three-sixteenths of an inch spaced one-fourth of an inch on centers. The holes or perforations should be arranged so that it will be difiicult to run a substantially straight line on the perforated sheet without coming into contact with at least one of the perforations in a relatively short distance.

It is preferable'that the separations in the finished sheet describe a circular path, or at least a closed curved path. By staggering the arrangement of such separations, and placing them relatively close together, an initial tear will lengthen only a short distance before it reaches a separation. The tear then tends to proceed along the path'of the separation. Because the separation is short and describes a closed path, the tear is restricted in its progress to the area defined by the closed path. In order to proceed farther, it would be necessary to start a new tear inthe outer perforated layer. A curved path for the separation is less conducive to tearing than an angular path which has a discontinuous break in its length.

The relatively short length of a tear which occurs in this material permits the application of a relatively small patch to repair it. The outer surface of the material is smooth enough to accommodate a vulcanized patch or a patch secured by self-curing cement, with effective results.

My invention contemplates within its scope the principle of forming in a vulcanized rubber material a plurality of separations or readily separable unions forming marginal Walls which operate to minimize tearing of the rubber sheet.

While I have shown and described certain present preferred embodiments of my invention, it is to be understood that it may be otherwise embodied and practiced within the spirit thereof and the scope of the appended claims.

Having thus described myinvention. what I claim and desire to protect byLetters Patent is:

.1. In a method of forming a wall of tear resisting vulcanizedrubber, the steps comprising forming a sheet of unvulcanized rubber, forming a perforated sheet of unvulcanized rubber, placing the sheets together in laminated relation, treating'at least the Walls of the perforations in'said perforated sheet to reduce their adhesive characteristic, and vulcanizing the sheets under 7 pressure.

2. In a method of forming a wall of tear resisting vulcanized rubber, the steps comprising form- It is desirable,

lar length of unvulcanized rubber, applying a layer of perforated rubber stock to the tubular length of rubber, treating the Walls of the perforations in said perforated layer to reduce their adhesive characteristic, joining the ends of the tubular length of rubber to form an annular member, flowing rubber from portions of said tubular length into perforations of said perforated stock, and vulcanizing the assembly under 10 pressure.

ALFRED N. IKNAYAN. 

